This invention relates to a method of joining piping materials, which is suitable for joining two thin-wall stainless steel pipes and for joining a metallic pipe and a metallic pipe coupling.
There has usually been practiced as a method for joining piping material such as metallic pipes, pipe couplings, etc. to thread end portions of the piping materials and screw one piping material into the other. However, such method has not been satisfactory with respect to workability, pressure resistance, airtightness, etc. Under such circumstances, the present applicant has previously invented a joining method to form a diametrally enlarged portion at an end portion of one piping material, i.e. a tapered portion, to which an annular gasket having a wedge-shaped cross-section is interposed and further an end portion of the other piping material is inserted, followed by application of pressure from the periphery to achieve plastic deformation of the diametrally enlarged portion and proposed it in Japanese Provisional Patent Publication No. 130729/1982.
However, in the piping materials having been joined according to such method, for example, using stainless steel pipes each having an outer diameter of 22.2 mm and a wall thickness of 1.0 mm, and an ethylene propylene rubber as the annular gasket, the piping materials exhibit a pressure resistance of about 30 kgf/cm.sup.2 and a pull-out resistance of about 100 kgf. Accordingly, there has been desired a method of joining piping materials to be developed, according to which the piping materials can be joined with superior airtightness, pressure resistance and pull-out resistance.